清解释Bush was born with a silver foot in his mouth.

这个解释起来有点麻烦,待我慢慢说来.
首先,有这样两个习语：一个是be born with a silver spoon in one's mouth,意思是门第高贵,出生富豪.另一个是put one's foot in one's mouth,直译的话是“把自己的脚放进自己的嘴里”,但引申义意思却是“说错话”.这个习语是从另一个习语put one’s foot in it衍生出来的.Put one’s foot in it本来是指一不小心一脚踩在污水或比污水更加厉害的东西上面,现在英国人也直接用这个习语来表达“说错话”.put one’s foot in one’s mouth就是一不小心一脚踩在自己的嘴巴上了,也就是说错话,美国人更习惯这种用法.你说的“口才差”只是一个其中意思,还有“说错话”,“失言”等含义.
然后,再看你问的这句话,Bush was born with a silver foot in his mouth.这句话中,把spoon换成了foot,而导致句意大变.本来说布什出身豪门,但却变成了“出生时脚就在嘴巴里”,而且是个“silver foot（银脚）”,讽刺意味极强!
不知你是否满意,